The Pentagon on Monday sent lawmakers a lengthy list of nearly $12.9 billion in unobligated military construction funds that could be raided to build more barriers on the U.S.-Mexico border as part of President Donald Trump's national emergency.

The move comes after Democrats accused Acting Defense Secretary Pat Shanahan of stonewalling lawmakers on whether military projects in their states are at risk.

Rep. Joaquin Castro said Monday that his phone calls to Sen. John Cornyn on legislation to block the government seizure of Texans' land went unreturned, countering the Texas senator's claim that the two lawmakers and potential 2020 Senate race rivals had never worked together.

"@JohnCornyn - I’m the one who called you last week to ask you to vote for my bill against giving away hundreds of miles of Texas land to the federal government in a Washington power grab," Castro (D-Texas) wrote in the tweet. "You never called me back. I don’t feel bad though; I hear it happens to lots of Texans."

Donald Trump issued the first veto of his presidency Friday afternoon, rejecting a congressional resolution that would have blocked him from funding his border wall without congressional approval.

“Consistent with the law and the legislative process designed by our founders, today I am vetoing this resolution,“ Trump said. “Congress has the freedom to pass this resolution, and I have the duty to veto it. And I'm very proud to veto it.”

Two weeks ago, Sen. Thom Tillis said President Donald Trump’s national emergency declaration violated the separation of powers and created a dangerous precedent, stating in an op-ed that he would vote to reverse it.

On Thursday, the North Carolina Republican flipped and sided with Trump on the border vote.

On Thursday morning, President Donald Trump sent out a pointed missive ahead of the Senate’s vote to block his emergency declaration: “A vote for today’s resolution by Republican Senators is a vote for Nancy Pelosi, Crime, and the Open Border Democrats!“

Soon after, White House aides began blasting the tweet to GOP senators by text message to remind them of how the president viewed the impending vote, according to senators and aides who received the messages.

The Trump administration may send a volunteer emergency response team to assist with security and humanitarian efforts at the U.S.-Mexico border, according to four current and former officials briefed on the discussions.

With border arrest numbers on the rise, the Trump administration has been “casting about” for ways to devote additional resources to stem the flow of migrants, according to an official of the Department of Homeland Security who is familiar with the discussions.

Homeland Security Secretary Kirstjen Nielsen said Tuesday that congressional opposition to her department's border security measures makes her "fear for our democracy," insisting that members of Congress focus on changing the law instead of asking DHS to change how it is enforced.

“I said it before, but I really fear for our democracy when the body who creates the laws is telling the body who enforces the law, ‘just don't enforce the law,’” Nielsen said in an interview with Fox News. “If they don't like the law they should change it, but the men and women at the Department of Homeland Security have sworn an oath to protect communities to secure the homeland and to enforce the law that Congress passed.”

President Donald Trump invited some Senate Republicans to the White House on Wednesday afternoon for a two-hour conversation about trade. But the president couldn’t quite get the looming GOP rebuke of his national emergency declaration off his mind.

“He would like for us to vote against the [resolution]. But he understands and respects that senators may have different opinions,” said Sen. Lamar Alexander (R-Tenn.), who has yet to announce his position but has repeatedly griped about the president’s end run around Congress.

President Donald Trump scuttled a final effort by Senate Republicans to avoid an intraparty clash on his emergency declaration this week, a move that could juice the number of GOP senators that vote to rebuke Trump on the floor.

The president delivered the news in a phone call to Sen. Mike Lee (R-Utah) during a Republican lunch on Wednesday, according to three people familiar with the call. Trump told the Utah senator that he would not be able to endorse Lee's effort to change the National Emergencies Act to require congressional approval of emergency declarations — derailing a push by Republicans to find some way out of a confrontation with the president.

On the eve of Congress’ unprecedented rebuke of President Donald Trump, a majority of voters continue to oppose his declaration of a national emergency at the southern border, according to a POLITICO/Morning Consult poll.

The poll shows that Trump has failed to build support for his declaration in the face of congressional opposition; the results are essentially unchanged since he signed an order to reallocate military funds toward construction of a wall along the U.S.-Mexico border. Only 38 percent of voters support the declaration, the poll shows, down 1 percentage point from three weeks ago.

Senate Republicans are unlikely to be permitted to dramatically amend the House-passed resolution that would overturn the president’s national emergency, suggesting they will be confronted with a simple referendum on the president’s controversial declaration later this week.

The Senate parliamentarian is expected to allow few if any significant amendments at a majority threshold, according to people familiar with conversations with parliamentary staff. Some GOP senators, like Pat Toomey of Pennsylvania, have been seeking to modify the resolution to profess alarm at the situation on the southern border and proclaim support for a wall even as senators pan the president’s end run around Congress.

Senate Republicans are trying to head off a collision with President Donald Trump over the border wall this week, even as his new budget demands ensure the painful political battle will extend into the fall.

Some GOP senators are discussing a potential compromise with the White House in order to limit Republican defections on a vote this week to overturn Trump’s emergency declaration, according to GOP senators and aides. The matter was unresolved as of Monday evening, senators said, but the discussions underscore the reluctance of the GOP to fight with the president on the Senate floor.

President Donald Trump will ask Congress for another $8.6 billion on Monday to complete a 722-mile border wall, a senior administration official told POLITICO.

The president will make the request in his budget proposal for the upcoming fiscal year, which ends just one month before the 2020 presidential election. The sum — billions of dollars higher than the $5.7 billion demand that sparked the 35-day government shutdown — will surely divide spending negotiators again this year, likely resulting in static funding levels for much of the rest of the government or another lapse.

President Donald Trump on Saturday branded former ally Ann Coulter a “Wacky Nut Job” — less than a month after he insisted he did not follow the conservative commentator and blamed journalists for exaggerating her influence over White House decision-making.

“Wacky Nut Job @AnnCoulter, who still hasn’t figured out that, despite all odds and an entire Democrat Party of Far Left Radicals against me (not to mention certain Republicans who are sadly unwilling to fight), I am winning on the Border,” Trump tweeted.

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Sen. Ron Johnson made no secret of his displeasure with Donald Trump declaring a national emergency to build his border wall, worrying in late January that the president would take the “Emergency Act beyond where it’s ever been.”

But the Wisconsin Republican has made up his mind when it comes to voting on the House’s disapproval resolution next week. He’s standing with Trump.